MP3 Editting

[hatman]

Alas, I have not had an opportunity to even look at this. Rather frustrating, as I cannot install any sort of audio editing software in my machine at work, due to various security restrictions. We've had a variety of staff reductions here, which has reduced my flexibility to play with fun stuff like this in my free time. This is a long term project anyway. you looking to help, or looking to "borrow"? <|;O)

 

[hatman]

An update for anyone following this:

1) I have accumulated a 3-ring binder full of printouts from various web resources, mostly doctoral thesis papers. One of the annoying pieces of misinformation I have run into is the fact that someone somewhere along the lines asserted that every physical audio frame stores 1152 samples, and goes on to provide a simplified framesize calculation based on this assumption. And almost every white-paper or article in existence blindly reprints this, perhaps because it's USUALLY true, or perhaps it's an oversight in favor of concentrating on more complex concepts. For anyone who cares, this page gives just about the best info for decoding the header information for an physical frame: MPEG Audio Frame Header - CodeProject.

2) As hard as it was to figure out the header information, delving into the Side Information, which actually defines how the audio data is stored, is even more difficult to figure out. One of the best online resources I have found was here: http://www.mp3-tech.org/programmer/docs/mp3_theory.pdf. Right now, I am embroiled in decoding the side info, and using the Main_Data_Begin field to translate the Physical Audio Frames to Virtual Audio Frames, or a bitstream... not sure what is going to work out better.

3) After I have unpacked the audio frames, next comes the Huffman encoding. Every resource explains the CONCEPT of Huffman Encoding in greater or lesser detail, because it is this encoding that actually reduces filesize by up to a factor 12 while still maintaining CD audio quality. It uses 32 lookup tables to represent blocks of audio data, and finding those tables for download is almost impossible. I finally located an open source software that contained the tables in a format I could work with: Index of /~ruckert/understanding_mp3/distribution/32bit.

4) I have gotten deep enough into this to realize that this project may be far too ambitious for my programming skills... or maybe for my patience, I don't know which. I'm still pushing forward, as time allows, and each time I see a road-block in the distance, it seems to fall away as I get closer.

 

[iknowu99]

thanks for the post! I was curious about how shazam works (borrow) and if it would be possible to understand it through vba but we might need some reading up on sound engineering...

 

[CheesyHome]

how can it would be possible to VBA ?
Thanks
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[hatman]

how can it would be possible to VBA ?
Thanks

Welcome to the BOARD!

I assume that you are questioning how one approaches this task in VBA. Or perhaps any complex project that seems to be unrelated to Excel? In a very real sense, VBA has most of the functionality of VB 6.0, making it a very powerful programming language, though uncompiled, so it does tend to run somewhat slow compared to code compiled to take advantage of multi-threading. Any capability that is not intrinsically available within the VBA library can usually be accessed a) from another library, b) from the Windows API (Windows .dll files), or c) Built from scratch. In the case of "playing music" one needs to communicate with the sound card. So far, this looks like it will be one of the more difficult parts of this particular project... I haven't solved it yet, but I continue to research it, as time permits. This is a long-term project that I am doing as a way to challenge myself. It's an extension of a project I built several years ago that allows editing of ID3 Tags and embedding cover-art images in MP3 Files... all in Excel.